Prior art isostatic presses as a rule comprise a frame surrounding a cylindrical pressure vessel the longitudinal axis of which is vertical. At the top and bottom ends of the vessel there are end plugs. The lower end plug often forms an integral bottom whereas the top plug is removable for the purpose of permitting introduction of the charge and removal of the pressed articles. Accordingly, when the top plug is to be removed, the vessel must be separated from the frame which is achieved by lateral displacement of either the vessel or the frame. Before such displacement can be carried out it is, however, obviously necessary to create a clearance between the top plug and the frame. This clearance can be created in the way that the top plug, which has threads engaging corresponding threads in the jacket of the vessel, is rotated so that it is displaced downwards. It is, however, important to note that this solution is practical only in respect of relatively small vessels.
When the vessel has been displaced relative to the frame and the top plug removed, the finished articles are taken out, whereupon a further charge is introduced. Then the top plug is again mounted, whereupon the vessel is again brought into force-transmitting contact with the frame. Finally, the interior of the vessel is pressurized so that isostatic pressing occurs. After depressurization the cycle above described is repeated. As is understood, that cycle comprises several steps which have to be carried out manually. For that reason this type of cycle is comparatively time-consuming and cannot be automated. This explains why it has not so far been commercially realistic to use isostatic presses for the manufacture of mass produced articles. On the other hand, the isostatic pressing method has several inherent advantages which makes that method interesting also in the just-mentioned context. An example of such a potential field of use is the manufacture of piston rods for small and medium sized internal combustion engines. Experiments have been conducted for the purpose of manufacturing such connecting rods with the use of prior art isostatic presses but it has turned out that, in comparison with conventional presses, the productivity is too low to be tolerable from an economical point of view.
ONE OF THE POTENTIAL INHERENT ADVANTAGES OF ISOSTATIC PRESSES ABOVE REFERRED TO IS THAT A VERY ACCURATE SHAPING OF THE PRESSED ARTICLES CAN BE GUARANTEED, SINCE THE FINAL DIMENSIONS OF THE PRESSED ARTICLES ARE ONLY DEPENDENT ON THE ACCURACY AT WHICH THE METAL POWDER TO BE PRESSED IS CHARGED. This charging can be carried out very accurately. Another major advantage stems from the possibility to precisely control and, if necessary, also to change, the composition of the metal alloy used. This advantage is the result of the fact that the corresponding problem is, in the isostatic pressing technique, reduced to correctly proportioning the relative amounts of the components making up the alloy.
The main object of the present invention is to provide an isostatic press having a productivity comparable to that of conventional drop forging presses. It should be appreciated that realization of that object means that the isostatic pressing method becomes equivalent to the conventional methods as far as manufacturing costs are concerned, the net advantage being the higher quality and lesser tolerances of the articles produced.